Development of an exposure apparatus using EUV (Extreme Ultra Violet) light (hereinafter, also “EUV exposure apparatus”) is underway so as to form downscaled semiconductor devices.
Because of the attenuation of the EUV light in the air, the interior of the EUV exposure apparatus is kept in a vacuum. In this case, the EUV exposure apparatus is unable to use a vacuum chuck, so that the EUV exposure apparatus includes an electrostatic chuck for fixing a semiconductor substrate. The electrostatic chuck is excellent in holding power and temperature control over the semiconductor substrate because the electrostatic chuck attracts the entire back surface of the semiconductor substrate.
However, when a foreign matter is present on a wafer stage, the surface of the semiconductor substrate is distorted because the electrostatic chuck attracts the semiconductor substrate in a state where the foreign matter is put between the wafer stage and the semiconductor substrate. When the EUV exposure apparatus exposes the semiconductor substrate to the EUV light in a state where the surface of the semiconductor substrate is distorted, a transferred pattern by the exposure to the light has a distortion in an opposite direction to that of the distortion of the semiconductor substrate generated during the attraction of the semiconductor substrate when the semiconductor substrate is unloaded from the wafer stage and the surface of the semiconductor substrate returns to an undistorted state.
To remove the foreign matter on the wafer stage, it is necessary to release the vacuum state of a chamber of the EUV exposure apparatus to release the interior of the chamber to the atmospheric pressure. Accordingly, it is impossible to remove the foreign matter on the wafer stage instantly or frequently.